Catheter with removable vision probe

ABSTRACT

A medical system may comprise a catheter having a main lumen and a distal tip positioned in a working configuration at a working location. The medical system may also comprise a sensor system coupled to the catheter to generate measurement signals. The medical system may also comprise a control system. The control system may be configured to receive the measurement signals from the sensor system. The control system may be operable to identify from the received measurement signals the working configuration of the distal tip of the catheter. The control system may be configured to control at least one degree of freedom of the distal tip of the catheter to maintain the working configuration of the distal tip of the catheter based on a selected stiffness mode and the received measurement signals. The selected stiffness mode determines the at least one degree of freedom of the distal tip.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 13/274,208 filed Oct. 14, 2011, which is incorporated herein byreference in its entirety. This patent document is related to andincorporates by reference the following co-filed patent applications:U.S. patent application Ser. No. 13/274,198, filed Oct. 14, 2011entitled “Catheters with Control Modes for Interchangeable Probes”; U.S.patent application Ser. No. 13/274,229 entitled “Vision Probe andCatheter Systems”; and U.S. patent application Ser. No. 13/274,237 filedOct. 14, 2011 entitled “Catheter Sensor Systems.”

BACKGROUND

Medical devices that navigate body lumens need to be physically smallenough to fit within the lumen. Lung catheters, for example, which maybe used to perform minimally invasive lung biopsies or other medicalprocedures, may need to follow airways that decrease in size as thecatheter navigates branching passages. To reach a target location in alung, a catheter may need to follow passages having diameters as smallas 3 mm or less. Manufacturing a catheter that includes the mechanicalstructures suitable for remote or robotic operation and that has adiameter that is sufficiently small to navigate such small lumens can bechallenging. In particular, one desirable configuration for remotelyoperated catheter would provide a tool mounted on a steerable segment;tendons or pull wires that extend down the length of the catheter to anexternal drive system that pulls on the tendons to actuate the tool orsteerable segment; lumens for suction and/or irrigation; a vision systemfor viewing of the target location; and sensors to identify the locationof the instrument relative to a patient's body. Accommodating all of thedesired features and elements of a lung catheter or other device havinga diameter about 3 mm or less can be difficult.

SUMMARY

In accordance with an aspect of the invention, a catheter system has aremovable vision probe that can be replaced with a biopsy probe or othermedical probe. The vision probe may be used for navigation to a worksite and then removed and replaced with the biopsy probe that takes atissue sample. The catheter system can thus provide a high level ofvision and medical functionality in a small diameter. Control logic forrobotic actuation of the catheter adjust for issues that may occur ifthe catheter moves while the tools or probes are swapped or if thepatient moves. In particular, when the vision probe is removed, feedbackcontrol and a distal sensor (such as a fiber-optic shape sensor) areused to maintain or return to the desired location or workingconfiguration for use of the biopsy probe. The feedback information fromthe sensor thus can be used to control the actuator tendons such thatthe working configuration of a distal tip of the catheter is maintainedeven under disturbances due to tool removal or anatomy motion. In thisway, accuracy of the catheter system is maintained and biopsy yield maybe improved. Instead of maintaining a constant working configuration,parameters of the desired working configuration can be recorded, and thecatheter can be straightened or relaxed for easier removal and insertionof probes and subsequently returned to the desired working configurationafter a new probe has been inserted or upon user indication.

One specific embodiment of the invention is a medical system including acatheter and control logic. The catheter includes a main lumen and amechanical system. The main lumen accommodates either a vision probe ora medical probe and is too narrow to simultaneously guide both a visionprobe and a medical probe to the distal tip. The control logic operatesthe mechanical system to control a pose of a distal tip of the catheter.In particular, the control logic can identify a desired workingconfiguration of the distal tip while the vision probe is deployed andcan hold or return the catheter to the desired working configurationwhen the vision probe has been removed from the catheter and the medicalprobe is deployed in the main lumen.

Another specific embodiment of the invention is a medical systemincluding a removable vision probe and a catheter. The catheter has alumen sized to guide either the vision system or a medical tool to adistal tip of the catheter. Further, the catheter has a width less thanabout 3 mm and is too narrow to simultaneously guide both the visionprobe and the medical probe to the distal tip.

Yet another embodiment of the invention is a process that includes:using a vision probe deployed in a catheter when identifying a workingconfiguration of a distal tip of the catheter; removing the vision probefrom the catheter; deploying a medical probe in place of the visionprobe that was removed; and actuating the catheter to maintain or returnto the working configuration of the distal tip when a medical probe isdeployed in the catheter in place of the vision probe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a robotic catheter system in accordance with an embodimentof the invention having multiple control modes.

FIG. 2 shows an embodiment of an actuated distal tip that can beemployed in the system of FIG. 1.

FIGS. 3A and 3B show cross-sectional views of proximal and distalsections of a catheter in accordance with an embodiment of theinvention.

FIG. 4 shows a cross-sectional view of a vision probe that may bedeployed in the catheter of FIGS. 3A and 3B and swapped out for use ofmedical probes in the catheter shown in FIGS. 3A and 3B.

FIG. 5 is a flow diagram of a process for using the catheter system witha removable vision system and multiple control modes.

FIG. 6 is a flow diagram of a catheter control process in a steeringmode.

Use of the same reference symbols in different figures indicates similaror identical items.

DETAILED DESCRIPTION

A catheter system can employ a vision probe that is interchangeable withone or more medical probes or tools. The vision probe can be removed andreplaced with a medical probe used in a medical procedure. Theinterchanging of the vision and medical probes may permit the cathetersystem to have a smaller diameter and thus navigate smaller passagesthan would a similar system that simultaneously accommodates both visionand medical systems. Alternatively, interchanging probes allow morespace for vision and medical systems having greater functionality thanmight a catheter that must simultaneously accommodate both vision andmedical systems.

One method for using a catheter system includes steering a catheteralong a body lumen for at least part of the path to a work site for amedical procedure. A vision system may then be deployed in the catheterduring the steering and/or used to view the work site reached whennavigation is complete. The vision system can also be used to helpidentify a desired working configuration for the catheter and whenmanipulating the catheter into the desired working configuration. Thecontrol system of the catheter can then record the working configurationand may be placed in a “holding” mode in which the pose of the catheterrelative to a patient is monitored and the catheter is actuated toactively maintain or return to the recorded working configuration. Thecontrol system may provide different types of control modes, which maybe useful for different types of medical probes or different types ofmedical procedures. For example, if the medical probe includes a laser,a combination of the location and orientation of the distal tip of thecatheter can be controlled so that the distal tip remains targeted on aspecific location in the patient. An alternative holding mode canmaintain the location of the distal tip of the catheter while permittingthe orientation of the distal tip to change or maintain a distal tipalong a line.

FIG. 1 schematically illustrates a catheter system 100 in accordancewith one embodiment of the invention. In the illustrated embodiment,catheter system 100 includes a catheter 110, a drive interface 120,control logic 140, an operator interface 150, and a sensor system 160.

Catheter 110 is a generally flexible device having one or more lumensincluding a main lumen that can accommodate interchangeable probes suchas described further below. Flexible catheters can be made using abraided structure such as a woven wire tube with inner or outer layersof a flexible or low friction material such as polytetrafluoroethylene(PTFE). In one embodiment, catheter 110 includes a bundle of lumens ortubes held together by a braided jacket and a reflowed (i.e., fused bymelting) jacket of a material such as Polyether Block Amide (Pebax).Alternatively, an extrusion of a material such as Pebax can similarly beused to form multiple lumens in catheter 110. Catheter 110 particularlyincludes a main lumen for interchangeable probe systems and smallerlumens for pull wires and sensor lines. In the illustrated embodiment,catheter 110 has a proximal section 112 attached to drive interface 120and a distal section 114 that extends from the proximal section 112. Anadditional steerable segment 116 (e.g., a metal structure such as shownin FIG. 2 and described further below) can form a distal subsection ofdistal section 114. Pull wires extend from drive system 120 throughproximal section 112 and distal section 114 and connect to steerablesegment 116.

The overall length of catheter 110 may be about 60 to 80 cm or longerwith distal section 114 being about 15 cm long and steerable segment 116being about 4 to 5 cm long. In accordance with an aspect of theinvention, distal section 114 has a smaller diameter than does proximalsection 112 and thus can navigate smaller natural lumens or passages.During a medical procedure, at least a portion of proximal section 112and all of distal section 114 may be inserted along a natural lumen suchas an airway of a patient. The smaller diameter of distal section 114permits use of distal section 114 in lumens that may be too small forproximal section 112, but the larger diameter of distal section 114facilitates inclusion of more or larger structures or devices such aselectromagnetic (EM) sensors 162 that may not fit in distal section 114.

Steerable segment 116 is remotely controllable and particularly has apitch and a yaw that can be controlled using pull wires. Steerablesegment 116 may include all or part of distal section 114 and may besimply implemented as a multi-lumen tube of flexible material such asPebax. In general, steerable segment 116 is more flexible than theremainder of catheter 110, which assists in isolating actuation orbending to steerable segment 116 when drive interface 120 pulls onactuating tendons. Catheter 110 can also employ additional features orstructures such as use of Bowden cables for actuating tendons to preventactuation from bending proximal section 112 (or bending any portion thesection of 114 other than steerable segment 116) of catheter 110. FIG. 2shows one specific embodiment in which steerable segment 116 is madefrom a tube 210 that in catheter 110 of FIG. 1 contains multiple tubesdefining a main lumen for a probe system and smaller lumens foractuation tendons 230 and a shape sensor not shown in FIG. 2. In theillustrated embodiment, tendons 230 are placed 90° apart surroundinglumen 312 to facilitate steering catheter 110 in pitch and yawdirections defined by the locations of tendons 230. A reflowed jacket,which is not shown in FIG. 2 to better illustrate the internal structureof steerable segment 116, may also cover tube 210. As shown in FIG. 2,tube 210 is cut or formed to create a series of flexures 220. Tendons230 connect to a distal tip 215 of steerable segment 116 and extend backto a drive interface 120. Tendons 230 can be wires, cables, Bowdencables, hypotubes, or any other structures that are able to transferforce from drive interface 120 to distal tip 215 and limit bending ofproximal section 112 when drive interface 120 pulls on tendons 230. Inoperation, pulling harder on any one of tendons 230 tends to causesteerable segment 116 to bend in the direction of that tendon 230. Toaccommodate repeated bending, tube 210 may be made of a material such asNitinol, which is a metal alloy that can be repeatedly bent with littleor no damage.

Drive interfaces 120 of FIG. 1, which pulls on tendons 230 to actuatesteerable segment 116, includes a mechanical system or transmission 124that converts the movement of actuators 122, e.g., electric motors, intomovements of (or tensions in) tendons 230 that run through catheter 110and connect to steerable segment 116. (Push rods could conceivably beused in catheter 110 instead of pull wires but may not provide adesirable level of flexibility.) The movement and pose of steerablesegment 116 can thus be controlled through selection of drive signalsfor actuators 122 in drive interface 120. In addition to manipulatingtendons 230, drive interface 120 may also be able to control othermovement of catheter 110 such as range of motion in an insertiondirection and rotation or roll of the proximal end of catheter 110,which may also be powered through actuators 122 and transmission 124.Backend mechanisms or transmissions that are known for flexible-shaftinstruments could in general be used or modified for drive interface120. For example, some known drive systems for flexible instruments aredescribed in U.S. Pat. App. Pub. No. 2010/0331820, entitled “CompliantSurgical Device,” which is hereby incorporated by reference in itsentirety. Drive interface 120 in addition to actuating catheter 110should allow removal and replacements of probes in catheter 110, so thatthe drive structure should be out of the way during such operations.

A dock 126 in drive interface 120 can provide a mechanical couplingbetween drive interface 120 and catheter 110 and link actuation tendonsto transmission 124. Dock 126 may additionally contain electronics forreceiving and relaying sensor signals from portions of sensor system 160in catheter 110 and contain an electronic or mechanical system foridentifying the probe or the type of probe deployed in catheter 110.

Control logic 140 controls the actuators in drive interface 120 toselectively pull on the tendons as needed to actuate and steer steerablesegment 116. In general, control logic 140 operates in response tocommands from a user, e.g., a surgeon or other medical personnel usingoperator interface 150, and in response to measurement signals fromsensor system 160. However, in holding modes as described further below,control logic 140 operates in response to measurement signals fromsensor system 160 to maintain or acquire a previously identified workingconfiguration. Control logic 140 may be implemented using a generalpurpose computer with suitable software, firmware, and/or interfacehardware to interpret signals from operator interface 150 and sensorsystem 160 and to generate control signals for drive interface 120.

In the illustrated embodiment, control logic 140 includes multiplemodules 141, 142, 143, and 144 that implement different processes forcontrolling the actuation of catheter 110. In particular, modules 141,142, 143, and 144 respectively implement a position stiffening mode, anorientation stiffening mode, a target position mode, and a target axialmode, which are described further below. A module 146 selects whichcontrol process will be used and may base the selection on user input,the type or status of the probe deployed in catheter 110, and the taskbeing performed. Control logic 140 also includes memory storingparameters 148 of a working configuration of steerable segment 116 thatis desired for a task, and each of the modules 141, 142, 143, and 144can uses their different control processes to actively maintain or holdthe desired working configuration.

Operator interface 150 may include standard input/output hardware suchas a display, a keyboard, a mouse, a joystick, or other pointing deviceor similar I/O hardware that may be customized or optimized for asurgical environment. In general, operator interface 150 providesinformation to the user and receives instructions from the user. Forexample, operator interface 150 may indicate the status of system 100and provide the user with data including images and measurements made bysystem 100. One type of instruction that the user may provide throughoperator interface 150, e.g., using a joystick or similar controller,indicates the desired movement or position of steerable segment 116, andusing such input, control logic 140 can generate control signals foractuators in drive interface 120. Other instructions from the user canselect an operating mode of control logic 140.

Sensor system 160 generally measures a pose of steerable segment 116. Inthe illustrated embodiment, sensor system 160 includes EM sensors 162and a shape sensor 164. EM sensors 162 include one or more conductivecoils that may be subjected to an externally generated electromagneticfield. Each coil of EM sensors 162 then produces an induced electricalsignal having characteristics that depend on the position andorientation of the coil relative to the externally generatedelectromagnetic field. in an exemplary embodiment, EM sensors 162 areconfigured and positioned to measure six degrees of freedom, e.g., threeposition coordinates X, Y, and Z and three orientation angles indicatingpitch, yaw, and roll of a base point. The base point in system 100 is ator near the end of proximal section 112 and the start of distal section114 of catheter 110. Shape sensor 164 in the exemplary embodiment of theinvention includes a fiber grating that permits determination of theshape of a portion of catheter 110 extending from the base point, e.g.,the shape of distal section 114 or steerable segment 116. Such shapesensors using fiber gratings are further described in U.S. Pat. No.7,720,322, entitled “Fiber Optic Shape Sensor” and U.S. Pat. No.7,930,065, entitled “Robotic Surgery System Including Position Sensorsusing Fiber Bragg Gratings,” which are hereby incorporated by referencein their entirety. An advantage of the illustrated type of sensor system160 is that EM sensors 162 can provide measurements relative to theexternally generated electrical field, which can be calibrated relativeto a patient's body. Thus, system 160 can use EM sensors 162 to reliablymeasure the position and orientation of a base point for shape sensor164, and shape sensor 164 need only provide shape measurement for arelatively short distance. Additionally, distal section 114 onlycontains shape sensor 164 and may have a diameter that is smaller thanthe diameter of proximal section 112. More generally, sensor system 160need only be able to measure the pose of steerable segment 116, andother types of sensors could be employed.

FIGS. 3A and 3B respectively show cross-sections of the proximal anddistal sections 112 and 114 of catheter 110 in one embodiment of theinvention. FIG. 3A shows an embodiment of catheter 110 having a body 310that includes a main lumen 312 for a vision or medical probe, lumens 314containing tendons 230, lumens 316 containing EM sensors 162 orassociated signal wires, and a lumen 318 containing a fiber shape sensor164. Main lumen 312, wire lumens 314, and a shape sensor lumen 318extend into distal section 114 as shown in FIG. 3B, but lumens 316 forEM sensors 162 are not needed in distal section 114 because EM sensors162 are only in proximal section 112, Accordingly, distal section 114can be smaller than proximal section 112. In an exemplary embodiment,body 310 in proximal section 112 has an outer diameter of about 4 mm(e.g., in a range from 3 to 6 mm) and provides main lumen 312 with adiameter of about 2 mm (e.g., in a range from 1 to 3 mm) and in distalsection 114 has an outer diameter of about 3 mm (e.g., in a range from 2to 4 mm) while maintaining the diameter of main lumen 312 at about 2 mm.A smooth taper (as shown in FIG. 1) or an abrupt step in body 310 can beused at the transition from the larger diameter of proximal section 112to the smaller diameter of distal section 116.

The specific dimensions described in above are primarily for a catheterthat accommodates probes having a diameter of 2 mm, which is a standardsize for existing medical tools such as lung biopsy probes. However,alternative embodiments of the invention could be made larger or smallerto accommodate medical probes with a larger or smaller diameter, e.g., 1mm diameter probes. A particular advantage of such embodiments is that ahigh level of functionality is provided in a catheter with relativesmall outer diameter when compared to the size of probe used in thecatheter.

FIGS. 3A and 3B also show a sheath 360 that may be employed betweencatheter body 310 and a probe in main lumen 312. In one embodiment ofcatheter 110, sheath 360 is movable relative to body 310 can be extendedbeyond the end of steerable segment 116. This may be advantageous insome medical procedures because sheath 360 is even smaller than distalsection 114 and therefore may fit into smaller natural lumens orpassages. For example, if catheter 110 reaches a branching of lumensthat are too small to accommodate steerable segment 116, steerablesegment 116 may be pointed in the direction of the desired branch, sothat sheath 360 can be pushed beyond the end of steerable segment 116and into that branch. Sheath 360 could thus reliably guide a medicalprobe into the desired branch. However, sheath 360 is passive in that itis not directly actuated or steerable. In contrast, distal section 114accommodates pull wires 230 that connect to steerable segment 116 andcan be manipulated to steer or pose steerable segment 116. In somemedical applications, the active control of steerable segment 116 isdesirable or necessary during a medical procedure, and passive sheath360 may not be used in some embodiments of the invention.

Main lumen 312 is sized to accommodate a variety of medical probes. Onespecific probe is a vision probe 400 such as illustrated in FIG. 4.Vision probe 400 has a flexible body 410 with an outer diameter (e.g.,about 2 mm) that fits within the main lumen of catheter 110 and withmultiple inner lumens that contain the structures of vision probe 400.Body 410 may be formed using an extruded flexible material such asPebax, which allows creation of multiple lumens. In the illustratedembodiment, the structure of vision probe 400 includes a CMOS camera420, which is at the distal end of the probe and connected through oneor more signal wires (not shown) that extend along the length of visionprobe 400, e.g., to provide a video signal to control logic 140 oroperator interface 150 as shown in FIG. 1. Vision probe 400 alsoincludes illumination fibers 430 that provide light for imaging within abody lumen and fluid ports 326 for suction and irrigation that may beuseful, for example, for rinsing of a lens of camera 420. Vision probe400 may additionally include an electromagnetic sensor (not shown)embedded just proximally to camera 420 to provide additional poseinformation about the tip of vision probe 400.

Vision probe 400 is adapted to be inserted or removed from catheter 110while catheter 110 is in use for a medical procedure. Accordingly,vision probe 400 is generally free to move relative to catheter 110.While movement relative to catheter 110 is necessary or desirable duringinsertion or removal of vision probe 400, the orientation of a visionprobe 400 (and some medical probes) may need to be known for optimal oreasier use. For example, a user viewing video from vision probe 400 andoperating a controller similar to a joystick to steer catheter 110generally expects the directions of movement of the controller tocorrespond to the response of steerable segment 116 and the resultingchange in the image from vision probe 400. Operator interface 150 needs(or at least can use) information on the orientation of vision probe 400relative to tendons 230 in order to provide a consistency in directionsused in the user interface. In accordance with an aspect of theinvention, a keying system (not shown) can fix vision probe 400 into aknown orientation relative to catheter 110 and tendons 230. The keyingsystem may, for example, include a spring, fixed protrusion, or latch onvision probe 400 or steerable segment 116 and a complementary notch orfeature in steerable segment 116 or vision probe 400.

Vision probe 400 is only one example of a probe system that may bedeployed in catheter 110 or guided through catheter 110 to a work site.Other probe systems that may be used include, but are not limited to,biopsy forceps, biopsy needles, biopsy brushes, ablation lasers, andradial ultrasound probes. In general, catheter 110 can be used withexisting manual medical probes that are commercially available frommedical companies such as Olympus Europa Holding GmbH.

The catheter system 100 of FIG. 1 can be used in procedures that swap avision probe and a medical probe. FIG. 5 is a flow diagram of oneembodiment of a process 500 for using the catheter system 100 of FIG. 1.In process 500, vision probe 400 is deployed in catheter 110 in step510, and catheter 110 is inserted along a path including a natural lumenof a patient. For example, for a lung biopsy, steerable segment 116 ofcatheter 110 may be introduced through the mouth of a patient into therespiratory tract of the patient. Vision probe 400 when fully deployedin catheter 110 may fit into a keying structure that keeps vision probe400 in a desired orientation at or even extending beyond steerablesegment 116 to provide a good forward view from the steerable segment116 of catheter 110. As noted above, steerable segment 116 of catheter110 is steerable, and vision probe 320 can provide video of therespiratory tract that helps a user when navigating catheter 110 towarda target work site. However, use of vision probe 400 during navigationis not strictly necessary since navigation of catheter 110 may bepossible using measurements of sensor system 160 or some other systemwith or without vision probe 400 being deployed or used in catheter 110.The path followed to the work site may be entirely within natural lumenssuch as the airways of the respiratory track or may pierce and passthrough tissue at one or more points.

When steerable segment 116 reaches the target work site, vision probe400 can be used to view the work site as in step 530 and to posesteerable segment 116 for performance of a task at the target work siteas in step 540. Posing of steerable segment 116 may use images or visualinformation from vision probe 400 and measurements from sensor system160 to characterize the work site and determine the desired workingconfiguration. The desired working configuration may also depend on thetype of tool that will be used or the next medical task. For example,reaching a desired working configuration of catheter 110 may bring thedistal tip of steerable segment 116 into contact with tissue to betreated, sampled, or removed with a medical tool that replaces visionprobe 400 in catheter 110. Another type of working configuration maypoint steerable segment 116 at target tissue to be removed using anablation laser. For example, tissue could be targeted in one or more 2Dcamera views white vision probe 400 is still in place in catheter 110,or target tissue can be located on a virtual view of the work site usingpre-operative 3D imaging data together with the position sensingrelative to patient anatomy. Still another type of working configurationmay define a line for the insertion of a needle or other medical toolinto tissue, and the working configuration includes poses in which thedistal tip of steerable segment 116 is along the target line. Ingeneral, the desired working configuration defines constraints on theposition or the orientation of the distal tip of steerable segment 116,and the shape of more proximal sections of catheter 110 is not similarlyconstrained and may vary as necessary to accommodate the patient.

Step 550 stores in memory of the control logic parameters that identifythe desired working configuration. For example, the position of a distaltip or target tissue can be defined using three coordinates. A targetline for a need can be defined using the coordinates of a point on theline and angles indicating the direction of the line from that point. Ingeneral, control logic 120 uses the stored parameters that define thedesired working configuration when operating in a holding mode thatmaintains steerable segment 116 of catheter 110 in the desired workingconfiguration as described further below.

Step 560 selects and activates a holding mode of the catheter systemafter the desired working configuration has been established andrecorded. Control logic 140 for catheter 110 of FIG. 1 may have one ormore modules 141, 142, 143, and 144 implementing multiple stiffeningmodes that may be used as holding modes when the desired configurationof steerable segment 116 has fixed constraints. The available controlmodes may include one or more of the following.

1.) A position stiffness mode compares the position of the distal tip ofsteerable segment 116 as measured by sensor system 160 to a desired tipposition and controls the actuators to minimize the difference indesired and measured tip positions. The position stiffness mode mayparticularly be suitable for general manipulation tasks in which theuser tries to precisely control the position of the tip and forsituations where the distal tip contacts tissue.

2.) An orientation stiffness mode compares the measured orientation orpointing direction of the distal tip to a desired pointing direction ofthe distal tip and controls the actuators to minimize the difference indesired and actual tip pointing direction. This orientation stiffeningthat may be suitable, e.g., when controlling an imaging device such asvision probe 400 attached steerable segment 116, in which case theviewing direction is kept as desired, while the exact position ofsteerable segment 116 may be less important.

3.) A target position stiffness mode uses a combination of the measuredtip position and pointing direction to control catheter 110 to alwayspoint the distal tip of steerable segment 116 towards a specified targetpoint some distance in front of steerable segment 116. In case ofexternal disturbances, control logic 140 may control the actuators toimplement this target position stiffening behavior, which may besuitable, e.g., when a medical probe inserted though the cathetercontains an ablation laser that should always be aimed at a targetablation point in tissue.

4.) A target axial motion stiffness mode uses a combination of themeasured tip position and pointing direction to ensure that the distaltip of steerable segment 116 is always on a line in space and has apointing direction that is also along that tine. This mode can beuseful, e.g., when inserting a biopsy needle along a specified line intotissue. Tissue reaction forces could cause the flexible section ofcatheter 110 to bend while inserting the needle, but this controlstrategy would ensure that the needle is always along the right line.

The selection of a mode in step 560 could be made through manualselection by the user, based on the type of probe that is being used(e.g., grasper, camera, laser, or needle) in catheter 110, or based onthe activity catheter 110 is performing. For example, when a laser isdeployed in catheter 110, control logic 120 may operate in positionstiffness mode when the laser deployed in catheter 110 is off andoperate in target position stiffness mode to focus the laser on adesired target when the laser is on. When “holding” is activated,control logic 140 uses the stored parameters of the workingconfiguration (instead of immediate input from operator interface 150)in generating control signals for drive interface 120,

The vision probe is removed from the catheter in step 570, which clearsthe main lumen of catheter 110 for the step 580 of inserting a medicalprobe or tool through catheter 110. For the specific step order shown inFIG. 5, control logic 140 operates in holding mode and maintainssteerable segment 116 in the desired working configuration while thevision system is removed (step 570) and the medical probe is inserted(step 580). Accordingly, when the medical probe is fully deployed, e.g.,reaches the end of steerable segment 116, the medical probe will be inthe desired working configuration, and performance of the medical taskas in step 590 can be then performed without further need or use of theremoved vision probe. Once the medical task is completed, the cathetercan be taken out of holding mode or otherwise relaxed so that themedical probe can be removed. The catheter can then be removed from thepatient if the medical procedure is complete, or the vision or anotherprobe can be inserted through the catheter if further medical tasks aredesired.

In one alternative for the step order of process 500, catheter 110 maynot be in a holding mode while the medical probe is inserted but can beswitched to holding mode after the medical probe is fully deployed. Forexample, catheter 110 may be relaxed or straightened for easy remove ofvision probe 400 (step 570) and insertion of the medical probe (step580). Once holding mode is initiated, e.g., after insertion of themedical probe, control logic 140 will control the drive interface 130 toreturn steerable segment 116 to the desired working configuration ifsteerable segment 116 has moved since being posed in the desired workingconfiguration. Thereafter, control logic 140 monitors the pose ofsteerable segment 116 and actively maintains steerable segment 116 inthe desired working configuration while the medical task is performed instep 590.

FIG. 6 shows a flow diagram of a process 600 of a holding mode that canbe implemented in control logic 140 of FIG. 1. Process 600 begins instep 610 with receipt of measurement signals from sensor system 160. Theparticular measurements required depend on the type of holding modebeing implemented, but as an example, the measurements can indicateposition coordinates, e.g., rectangular coordinates X, Y, and Z, of thedistal tip of steerable segment 116 and orientation angles, e.g., anglesθ_(X), θ_(Y), and θ_(Z), of a center axis of the distal tip of steerablesegment 116 relative to coordinate axes X, Y, and Z. Other coordinatesystems and methods for representing the pose of steerable segment 116could be used, and measurements of all coordinates and direction anglesmay not be necessary. However, in an exemplary embodiment, sensor system160 is capable of measuring six degrees of freedom (DoF) of the distaltip of steerable segment 116 and of providing those measurements tocontrol logic 140 in step 610.

Control logic 140 in step 620 determines a desired pose of steerablesegment 116. For example, control logic 140 can determine desiredposition coordinates, e.g., X′, Y′, and Z′, of the end of steerablesegment 116 and desired orientation angles, e.g., angles θ′_(X), θ′_(Y),and θ′_(Z) of the center axis of steerable segment 116 relative tocoordinate axes X, Y, and Z. The holding modes described above generallyprovide fewer than six constraints on the desired coordinates. Forexample, position stiffness operates to constrain three degrees offreedom, the position of the end of steerable segment 116 but not theorientation angles. In contrast, orientation stiffness mode constrainsone or more orientation angles but not the position of end of steerablesegment 116. Target position stiffness mode constrains four degrees offreedom, and axial stiffness mode constrains five degrees of freedom.Control logic 610 can impose further constraints to select one of set ofparameters, e.g., X′, Y′, and Z′ and angles θ′_(X), θ′_(Y), and θ′_(Z),that provides the desired working configuration. Such furtherconstraints include but are not limited to mechanical constraintsrequired by the capabilities of steerable segment 116 and of catheter110 generally and utilitarian constraints such as minimizing movement ofsteerable segment 116 or providing desired operating characteristicssuch as smooth, non-oscillating, and predictable movement withcontrolled stress in catheter 110. Step 620 possibly includes justkeeping a set pose steerable segment 116 by finding smallest movementfrom the measured pose to a pose satisfying the constraints, e.g.,finding the point on the target line closest to the measure position foraxial motion stiffness or finding some suitable pose from registeredpre-op data that is close to the current pose.

Control logic 140 in step 630 uses the desired and/or measured poses todetermine corrected control signals that will cause drive interface 120to move steerable segment 116 to the desired pose. For example, themechanics of catheter 110 and drive interface 120 may permit developmentof mappings from the desired coordinates X′, Y′, and Z′ and anglesθ′_(X), θ′_(Y), and θ′_(Z) to actuator control signals that provide thedesired pose. Other embodiments may use differences between the measuredand desired pose to determine corrected control signals. In general, thecontrol signals may be used not only to control actuators connectedthrough tendons to steerable segment 116 but may also control (to somedegree) insertion or roll of catheter 110 as a whole.

A branch step 650 completes a feedback loop by causing process 600 toreturn to measurement step 610 after control system 140 applies newcontrol signals drive interface 120. The pose of distal tip is thusactively monitored and controlled according to fixed constraints as longas control system 120 remains in the holding mode. It may be noted,however, that some degrees of freedom of steerable segment 116 may notrequire active control. For example, in orientation stiffness mode,feedback control could actively maintain pitch and yaw of steerablesegment 116, while the mechanical torsional stiffness of catheter 110 isrelied on hold the roll angle fixed. However, catheter 110 in generalmay be subject to unpredictable external forces or patient movement thatwould otherwise cause catheter 110 to move relative to the work site,and active control as in process 600 is needed to maintain or hold thedesired working configuration.

Some embodiments or elements of the above invention can be implementedin a computer-readable media, e.g., a non-transient media, such as anoptical or magnetic disk, a memory card, or other solid state storagecontaining instructions that a computing device can execute to performspecific processes that are described herein. Such media may further beor be contained in a server or other device connected to a network suchas the Internet that provides for the downloading of data and executableinstructions.

Although the invention has been described with reference to particularembodiments, the description is only an example of the inventionsapplication and should not be taken as a limitation. Various adaptationsand combinations of features of the embodiments disclosed are within thescope of the invention as defined by the following claims.

What is claimed is:
 1. A medical system comprising: a catheter having amain lumen and a distal tip configured to be positioned in a workingconfiguration at a working location; a sensor system coupled to thecatheter to generate measurement signals associated with the catheter; acontrol system, wherein the control system is configured to receive themeasurement signals from the sensor system, wherein the control systemis operable to identify from the received measurement signals theworking configuration of the distal tip of the catheter; and wherein thecontrol system is configured to control at least one degree of freedomof the distal tip of the catheter to maintain the working configurationof the distal tip of the catheter based on a selected stiffness mode andthe received measurement signals, and wherein the selected stiffnessmode determines the at least one degree of freedom of the distal tip ofthe catheter to be controlled by the control system.
 2. The medicalsystem of claim 1 wherein the distal tip of the catheter is steerable toadjust the working configuration of the distal tip.
 3. The medicalsystem of claim 1 wherein the catheter includes an isolated bendsection.
 4. The medical system of claim 3 wherein the isolated bendsection is formed with Nitinol.
 5. The medical system of claim 1 whereinthe catheter includes a mechanical system connected to control theworking configuration of the distal tip.
 6. The medical system of claim1 wherein the sensor system includes at least one of an electromagneticsensor or an optical fiber shape sensor.
 7. The medical system of claim1 further comprising a probe sized to extend within the main lumen,wherein the control system includes at least one of an electrical or amechanical system configured to identify the probe.
 8. The medicalsystem of claim 7 wherein the probe is removable from the main lumen. 9.The medical system of claim 7, further comprising a keying systemconfigured to fix the probe in a known orientation relative to thecatheter, wherein the keying system is configured to maintain the probein the known orientation when the probe is extended beyond the distaltip of the catheter.
 10. The medical system of claim 9, wherein thekeying system includes at least one of a spring, a fixed protrusion, alatch, or a notch associated with the probe and configured to cooperatewith a corresponding complementary notch or feature associated with thecatheter to fix the probe into the known orientation relative to thecatheter.
 11. The medical system of claim 1 wherein the sensor systemincludes a sensor component extending within a sensor lumen of thecatheter, the sensor lumen spaced apart from the main lumen.
 12. Themedical system of claim 1, wherein actuation tendons of the catheter aremechanically coupled with a transmission of a drive interface, whereinthe transmission converts movements of actuators into movements of theactuation tendons.
 13. The medical system of claim 1, wherein theselected stiffness mode includes at least one of: a position stiffnessmode configured to cause the control system to control the at least onedegree of freedom of the distal tip of the catheter based on acomparison of a measured position of the distal tip of the catheter anda desired tip position of the distal tip of the catheter; an orientationstiffness mode configured to cause the control system to control the atleast one degree of freedom of the distal tip of the catheter based on acomparison of a measured orientation of the distal tip of the catheterto a desired orientation of the distal tip of the catheter; a targetposition stiffness mode configured to cause the control system tocontrol the at least one degree of freedom of the distal tip of thecatheter based on the measured position of the distal tip of thecatheter and the measured orientation of the distal tip of the catheter;or a target axial motion stiffness mode configured to cause the controlsystem to control the at least one degree of freedom of the distal tipof the catheter based on the measured position of the distal tip of thecatheter and the measured orientation of the distal tip of the catheter.14. A method for operating a medical system, the method comprising:positioning a catheter in a working configuration at a working location,wherein the catheter has a main lumen and a distal tip; receiving, by acontrol system, measurement signals from a sensor system coupled to thecatheter and in communication with the control system; selecting astiffness mode, wherein the selected stiffness mode determines at leastone degree of freedom of the distal tip to be controlled by the controlsystem; identifying, by the control system, from the receivedmeasurement signals the working configuration of the distal tip;removing a first probe from the main lumen of the catheter; inserting asecond probe into the main lumen vacated by the first probe; andcontrolling, by the control system, at least one degree of freedom ofthe distal tip of the catheter to maintain the working configuration ofthe distal tip of the catheter based on the selected stiffness mode andthe received measurement signals.
 15. The method of claim 14 furthercomprising operating a mechanical system to control the workingconfiguration of the distal tip.
 16. The method of claim 14 whereinreceiving measurement signals from the sensor system includes receivingthe measurement signals from at least one of an electromagnetic sensoror an optical fiber shape sensor.
 17. The method of claim 14 wherein thefirst probe comprises a vision probe.
 18. The method of claim 17 furthercomprising: holding, by the control system, based on the selectedstiffness mode and the received measurement signals, the workingconfiguration during removal of the first probe and insertion of thesecond probe.
 19. The method of claim 17, further comprising fixing, bya keying system, the second probe in a known orientation relative to thecatheter, wherein the keying system is configured to maintain the secondprobe in the known orientation when the second probe is extended beyondthe distal tip of the catheter.
 20. The method of claim 19, wherein thekeying system includes at least one of a spring, a fixed protrusion, alatch, or a notch associated with the second probe and configured tocooperate with a corresponding complementary notch or feature associatedwith the catheter to fix the second probe in the known orientationrelative to the catheter.
 21. The method of claim 14, further comprisingmechanically coupling actuation tendons of the catheter with atransmission of a drive interface, wherein the transmission convertsmovements of actuators into movements of the actuation tendons.
 22. Themethod of claim 14, wherein selecting the stiffness mode includesselecting at least one of: a position stiffness mode configured to causethe control system to control the at least one degree of freedom of thedistal tip of the catheter based on a comparison of a measured positionof the distal tip of the catheter and a desired tip position of thedistal tip of the catheter; an orientation stiffness mode configured tocause the control system to control the at least one degree of freedomof the distal tip of the catheter based on a comparison of a measuredorientation of the distal tip of the catheter to a desired orientationof the distal tip of the catheter; a target position stiffness modeconfigured to cause the control system to control the at least onedegree of freedom of the distal tip of the catheter based on themeasured position of the distal tip of the catheter and the measuredorientation of the distal tip of the catheter; or a target axial motionstiffness mode configured to cause the control system to control the atleast one degree of freedom of the distal tip of the catheter based onthe measured position of the distal tip of the catheter and the measuredorientation of the distal tip of the catheter.